(a) Field of the Invention
The present invention relates to an aerobic biological process for treating waste sludges which are difficult to treat using conventional biological techniques. The process developed is applicable but not limited to waste sludges containing oils, greases, suspended materials and other such compounds as have been resistant to conventional biological treatment. The present invention is directed to the treatment of such concentrated waste sludges containing up to 60% suspended material through enzyme catalyzed extra-cellular biological reactions which are promoted in a properly acclimated colloidal process. In most cases the environmental impacts associated with the further treatment (if required) and disposal of the treatment residues are greatly lessened due to the order of magnitude reduction in organic contaminants and in biochemical oxygen demand which has occurred in the waste sludge.
(b) Description of Prior Art
The use of biological processes to treat water containing organic compounds at low concentrations has been well documented in the prior art. The use of activated sludge for treating municipal and industrial waste water involves the acclimation of populations of many species of micro-organisms, each playing an active part in the bio-degradation of the dissolved and un-dissolved compounds found in the sewage. However, the concentrations of compounds found in these systems are approximately two to three orders of magnitude lower than those encountered in the waste sludges mentioned above. Oil and grease contamination in these systems in excess of 100 parts per million (ppm) are not easily tolerated by the activated sludge systems. In addition, it is not common practice to operate these systems with suspended solids concentrations in excess of 10,000 ppm, and it is more normal to maintain these concentrations below 5,000 ppm to promote good operation of the process.
It is important at this point to distinguish between the waste sludges intended for disposal by the process according to this invention, and the term "activated sludge" which is often used in the prior art and can be misunderstood to mean treatment of sludge. Activated sludge is a medium which contains large populations of acclimated micro-organisms for the purpose of treating waste water. The activated sludge is mixed with in-coming waste water and provided with a suitably aerated environment in which the population of micro-organisms metabolize the organic matter in suspension and solution in the waste water.
The waste sludges destined for disposal by the process according to the invention contain few or non acclimated indigenous micro-organisms. This lack of acclimated indigenous micro-organisms and the refractory properties of the organic contaminants are the precise properties of the waste sludges being considered which make them difficult to treat biologically. In the past, these types of sludges have been subjected to land-farming applications whereby the indigenous micro-organisms eventually oxidize the contaminants and decrease their concentrations over a period of months or years, while often limiting the use of the land in question during a prescribed restriction period.
U.S. Pat. No. 4,749,494 describes a treatment process for the treatment of waste water with activated sludge which makes use of an ultra filtration membrane and involves a recirculation of liquid from the digestion tank to a reaction tank. The process is not suitable for treating oily wastes.
U.S. Pat. No. 4,584,102 describes the treatment of waste water and sludge, in which clean water, bacteria, nutrients and emulsifiers are used in a treatment unit constructed in a portion of a lagoon or impoundment.
U.S. Pat. No. 4,500,427 describes a treatment of waste water with activated sludge wherein the addition of air into the aeration tank is critical.
U.S. Pat. No. 4,430,225 describes the treatment of sewage using a special type tank.
It will be seen from a review of current literature that the above referenced activated sludge patents employ limited extra-cellular enzyme activity, generally characterized by holozoic nutrition, with intra-cellular enzymic digestion accompanied by active substrate transport for the treatment of the contaminants contained in the carriage waters. The acclimation period for such systems is short due to the abundance of species which readily acclimate to the contaminants in the waste water being treated. The formation of flocs within conventional activated sludge systems is primarily comprised of heterotrophic gram-negative bacteria.